The long range purpose of this project is to increase our understanding of the basic mechanisms of electrolyte movement across the endolymph-perilymph barrier in the guinea pig cochlea under normal conditions and under the influence of physical and chemical agents. The aim of current work is (1) to reveal electrolyte movement (Na ion, K ion, and Cl-) across the endolymph-perilymph barrier after exposure to intermediate levels of noise and (2) to correlate alteration of the ionic permeability of the cochlear partition with changes in sensitivity of the auditory organ.